This invention relates primarily to compositions for use as “anti-flutter compositions”. In the automotive industry, RHMAs may find application, for example as so called “anti-flutter” compositions, (i.e., to fill the space between the reinforcing structure of a vehicle part and the outer skin panels in order to lessen vibration), and as “sealer” adhesives for use in an automotive body shop or paint-shop (for example, to protect weld-points or flange/gaps from corrosive attacks and humidity, water, dust particles intrusion). They may also be used for other applications, for example to bond two metal or plastics substrates and/or to increase damping or stiffening. Currently, these functions are fulfilled by compositions with paste-like consistency, with a range of viscosity depending on the application. Generally, existing reactive compositions are based on rubber, PVC, or acrylics. For use in body-shops in the automotive industry, where parts can be oily, these compositions need to have enough viscosity/strength after application in order to withstand the panel degreasing and pre-treatment process (so called wash-off resistance to dipping and jet-spray of water/alkaline/dispersion solutions). This requirement for high viscosity limits the rate at which material can be supplied pumped to the application nozzle. Generally the tube length to the nozzle cannot exceed about 10 to about 15 meters. Since a single adhesive may be needed to be applied at several locations spread over hundreds of meters in an automotive plant, a specific dispensing system (pump and associated room area, equipment, drum storage and logistics) need to be installed for each location. Furthermore, even this high viscosity level is often not sufficient to guarantee resistance to wash-off in critical areas of the body, does not give enough green strength, and can not prevent de-localisation of the adhesive during the body-shop process if the part is compressed. A post-application curing to eliminate the above mentioned issues would affect the cycle time, space requirement, and quality of the parts produced. It would be desirable to provide materials which do not have the handling difficulties of viscous liquid compositions, but give good wash-off and squeeze resistance, for example by providing a hot melt adhesive in the form of pellets. Non-reactive hot melt adhesives (so-called “HMA”s) could be used for such applications. HMAs do not have a reactive curing step and accordingly will deform and lose adhesion when heated above their melting point after application. HMAs in general use are commonly based on EVA. U.S. Pat. No. 3,980,735 discloses a HMA comprising an ethylene-vinyl acetate (EVA) copolymer, an unsaturated alkyd resin and an organic peroxide which, according to the description in the patent, can be formulated into pellets and powders. The adhesive composition is not a reactive one however, because the peroxide is substantially fully reacted with the EVA copolymer during the formulation of the adhesive. RHMAs have been available since the 1980s. Because they are capable of curing to a thermosetting material, RHMAs eliminates or reduce many of the problems associated with conventional HMAs, such as poor heat resistance, and water or solvent permeation. The most common RHMAs are based on polyurethanes and are cured using water. There are also several other types of RHMA which are based on non-polyurethane moisture curable polymers or on polymers which are cured by reactive UV curing processes. WO-A-0172922 discloses thermoplastic polymer particle batches which are only homogenised immediately before use. They are applied immediately after they are homogenised, because after homogenisation, the reaction is initiated and the batches only have a limited pot life. WO-A-02090454 discloses granulated adhesive based on polyols and isocyanates which are mixed while excluding moisture. Both WO-A-01712922 and WO-A-02090454 rely on moisture as a curing mechanism which limits their pot life. GB-A-1299480 discloses a process for making joining tapes, using a hot melt adhesive containing solid particles of a tack resin, an ethylene copolymer, and a peroxide. U.S. Pat. No. 3,945,877 discloses adhesive compositions consisting of coal tar pitch, ethylene acrylic acid, ethylene vinyl acetate and a crosslinking agent (peroxide) for adhering surfaces.
RHMAs have been introduced, which are cured by the use of a free radical initiator such as a peroxide. RHMAs of this type comprising ethylene vinyl acetate (EVA) copolymers are now in use in the automotive industry. They are supplied in the form of a viscous fluid composition or a pasty composition which can be pumped into a dispensing gun for application. Examples of this type of RHMA include BETAGUARD™ supplied sealer compositions by The Dow Chemical Company. Such compositions often require the use of zinc acrylates as an adhesion promoter for metal which is undesirable because of Environmental, and Health and Safety concerns. Radical-initiated RHMAs generally have improved dimensional stability and strength and less tendency to sag, as well as better adhesion and corrosion resistance when heated to temperatures above their application temperature, as compared with other types of hot melt adhesive. One difficulty with viscous fluid compositions of this kind however is that the systems which are used for their dispensation and application are sensitive to the Theological properties of the compositions, which in turn depend on the temperature settings of the application equipment. The application equipment must therefore be set up differently for compositions with different Theological properties. This makes it difficult to deal with changes of formulation. In addition, viscous liquid RHMAs must be stored in small drums and processed with pumps through tubes and hoses for use. This produces large amounts of waste and high recycling costs.
It would be desirable to provide RHMA materials which do not have the handling difficulties of viscous liquid compositions, for example, by providing the RHMA in the form of pellets. In practice, however, pellets produced from RHMA compositions tend to be tacky and/or to have insufficient adhesion during initial application, particularly when applied to metal sheets under oily conditions, such as are typically encountered on a vehicle assembly line.